1. Technical Field
The present invention relates to a high-frequency receiver that enables good reception even in a reception area where there is a high possibility that a strong interference signal is received or an area where a television broadcast signal is weak.
2. Background Art
FIG. 6 shows a known high-frequency receiver. High-frequency receiver 1 includes high-frequency receiving unit 2 and demodulating unit 3 connected to an output terminal of high-frequency receiving unit 2.
In high-frequency receiving unit 2, a signal received by antenna 4 is input to amplifying circuit 5 through input terminal 2a. Amplifying circuit 5 amplifies the input signal and outputs the amplified signal as an output signal. The output signal is gain-controlled by amplifying circuit 6 and is then input to first input terminal 7a of mixer 7. An output signal of oscillator 8 is input to second input terminal 7b of mixer 7. Mixer outputs a frequency-converted signal. The output signal of mixer 7 is gain-controlled by amplifying circuit 9 and is then output from output terminal 10.
The signal output from output terminal 10 is gain-controlled in amplifying circuit 11 provided in demodulating unit 3. The output signal having been gain-controlled by amplifying circuit 11 is input to a digital filter and then to digital signal demodulator 12. Digital signal demodulator 12 demodulates the received signal and outputs the demodulated signal from output terminal 13.
Japanese Patent Unexamined Publication No. 2005-57642 is an example of the related art of the invention.
However, in known high-frequency receiver 1, if a high-level interference signal is input to input terminal 2a in a frequency area close to a desired input signal, amplifying circuit 5 or mixer 7 abnormally operates due to the high-level interference signal, which makes an input signal abnormal.
In particular, a recently introduced digital broadcast signal is controlled to have a low transmission output level as possible upon transmission from a transmissive antenna so as not to interfere with an existing analog broadcast signal. Accordingly, upon reception of the digital broadcast signal, a high-level analog broadcast signal may interfere with the digital broadcast signal, which results in the abnormal reception of signals.